For the geeky types out there, are you watching Raspberry Pi?
It’s a credit card sized Linux board for $25 (or $35 with more RAM). The size is pretty much limited by the connectors which include an HDMI output for your 66" digital television. Although intended for use in educational settings, my guess is the size and low price are going to start an avalanche of similar offerings over the next couple of years.
Wikipedia has a pretty good technical description and some photographs.
It will be available in single unit quantities later this month (they hope) but my guess is they will have way too many orders as soon as they open the flood gate. The initial production will probably be cleaned out really fast. Realistically, you should expect to put your order in as soon as you can and then wait several months.
Non-geeks should probably step back from the table. As it comes from the factory, the computer won’t do anything cute nor even mildly interesting. It will need some serious application software writing, hacking and slapping together of programs by Linux-types. No doubt the associated forum will be very helpful in such regards.
Regardless, I have no doubt that you’ll be seeing some interesting things in really small packages over the next year that use this and similar inspired-by super-mini computer boards.